Wind power, one the oldest and most established forms of alternative energy, might not be as green as we thought. A new study in the US has linked wind farms to local temperature rises of over 0.7°C—enough to change local weather and climate.

The study, published in Nature Climate Change, analyzed temperature changes around large wind farms in Texas, over the period from 2003 to 2011. The researchers found that temperatures around the farms increased by 0.72°C per decade. Writing in the journal, the researchers explain:

"We attribute this warming primarily to wind farms... These changes, if spatially large enough, may have noticeable impacts on local to regional weather and climate."

The heating, it's suggested, is a result of the energy created in the farms, as well as the movement and turbulence generated by turbine rotors. Interestingly, most of the heating occurs at night: it's speculated that, while the earth usually cools after the sun sets in turn bringing down the air temperature, the turbulence that the turbines produce keeps the ground around them warm for longer.

There's no denying that it's a small-scale study, but with the wind power industry big and growing—it produced 238 gigawatts of power last year, up by 21 percent over the previous year—it's a concerning finding. Perhaps most worrying is the fact that future wind farms are set to be bigger than those that have come before, which the researchers say would exacerbate the effects. The scientists plan to widen the scope of their research to assess other farms in the future. [Nature Climate Change]